Gabriele Cosmo
254 lines
9.5 KiB
C++
254 lines
9.5 KiB
C++
//
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// ********************************************************************
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// * License and Disclaimer *
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// * *
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// * The Geant4 software is copyright of the Copyright Holders of *
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// * the Geant4 Collaboration. It is provided under the terms and *
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// * conditions of the Geant4 Software License, included in the file *
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// * LICENSE and available at http://cern.ch/geant4/license . These *
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// * include a list of copyright holders. *
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// * *
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// * Neither the authors of this software system, nor their employing *
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// * institutes,nor the agencies providing financial support for this *
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// * work make any representation or warranty, express or implied, *
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// * regarding this software system or assume any liability for its *
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// * use. Please see the license in the file LICENSE and URL above *
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// * for the full disclaimer and the limitation of liability. *
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// * *
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// * This code implementation is the result of the scientific and *
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// * technical work of the GEANT4 collaboration. *
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// * By using, copying, modifying or distributing the software (or *
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// * any work based on the software) you agree to acknowledge its *
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// * use in resulting scientific publications, and indicate your *
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// * acceptance of all terms of the Geant4 Software license. *
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// ********************************************************************
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//
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//
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// -------------------------------------------------------------------
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//
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// GEANT4 Class header file
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//
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//
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// File name: G4PairProductionRelModel
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//
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// Author: Andreas Schaelicke
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//
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// Creation date: 02.04.2009
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//
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// Modifications:
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// 28-05-18 New version with improved screening function approximation, improved
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// LPM function approximation, efficiency, documentation and cleanup.
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// Corrected call to selecting target atom in the final state sampling.
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// (M. Novak)
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//
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// Class Description:
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//
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// Implementation of gamma convertion to e+e- in the field of a nucleus
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// relativistic approximation
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//
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// -------------------------------------------------------------------
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//
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#ifndef G4PairProductionRelModel_h
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#define G4PairProductionRelModel_h 1
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#include <CLHEP/Units/PhysicalConstants.h>
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#include "G4VEmModel.hh"
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#include "G4Log.hh"
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#include "G4Exp.hh"
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#include "G4Pow.hh"
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#include <vector>
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class G4ParticleChangeForGamma;
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class G4PairProductionRelModel : public G4VEmModel
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{
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public:
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explicit G4PairProductionRelModel(const G4ParticleDefinition* p = nullptr,
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const G4String& nam = "BetheHeitlerLPM");
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virtual ~G4PairProductionRelModel();
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virtual void Initialise(const G4ParticleDefinition*,
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const G4DataVector&) override;
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virtual void InitialiseLocal(const G4ParticleDefinition*,
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G4VEmModel* masterModel) override;
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virtual G4double ComputeCrossSectionPerAtom(
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const G4ParticleDefinition*,
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G4double kinEnergy,
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G4double Z,
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G4double A=0.,
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G4double cut=0.,
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G4double emax=DBL_MAX) override;
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virtual void SampleSecondaries(std::vector<G4DynamicParticle*>*,
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const G4MaterialCutsCouple*,
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const G4DynamicParticle*,
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G4double tmin,
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G4double maxEnergy) override;
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virtual void SetupForMaterial(const G4ParticleDefinition*,
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const G4Material*,G4double) override;
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inline void SetLPMflag(G4bool val) { fIsUseLPMCorrection = val; }
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inline G4bool LPMflag() const { return fIsUseLPMCorrection; }
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protected:
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// for evaluating screening related functions
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inline void ComputePhi12(const G4double delta, G4double &phi1, G4double &phi2);
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inline G4double ScreenFunction1(const G4double delta);
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inline G4double ScreenFunction2(const G4double delta);
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inline void ScreenFunction12(const G4double delta, G4double &f1, G4double &f2);
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// helper methods for cross-section computation under different approximations
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G4double ComputeParametrizedXSectionPerAtom(G4double gammaEnergy, G4double Z);
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G4double ComputeXSectionPerAtom(G4double gammaEnergy, G4double Z);
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G4double ComputeDXSectionPerAtom(G4double eplusEnergy, G4double gammaEnergy,
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G4double Z);
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G4double ComputeRelDXSectionPerAtom(G4double eplusEnergy, G4double gammaEnergy,
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G4double Z);
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private:
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// for creating some data structure per Z with often used comp. intensive data
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void InitialiseElementData();
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struct ElementData {
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G4double fLogZ13;
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G4double fCoulomb;
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G4double fLradEl;
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G4double fDeltaFactor;
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G4double fDeltaMaxLow;
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G4double fDeltaMaxHigh;
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G4double fEtaValue;
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G4double fLPMVarS1Cond;
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G4double fLPMILVarS1Cond;
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};
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// for precomputing comp. intensive parts of LPM suppression functions and
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// using them at run-time
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void InitLPMFunctions();
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void ComputeLPMGsPhis(G4double &funcGS, G4double &funcPhiS,
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const G4double varShat);
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void GetLPMFunctions(G4double &lpmGs, G4double &lpmPhis, const G4double sval);
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void ComputeLPMfunctions(G4double &fXiS, G4double &fGS, G4double &fPhiS,
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const G4double eps, const G4double egamma,
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const G4int izet);
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struct LPMFuncs {
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LPMFuncs() : fIsInitialized(false), fISDelta(100.), fSLimit(2.) {}
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G4bool fIsInitialized;
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G4double fISDelta;
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G4double fSLimit;
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std::vector<G4double> fLPMFuncG;
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std::vector<G4double> fLPMFuncPhi;
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};
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private:
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// hide assignment operator
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G4PairProductionRelModel & operator=
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(const G4PairProductionRelModel &right) = delete;
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G4PairProductionRelModel(const G4PairProductionRelModel&) = delete;
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protected:
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static const G4int gMaxZet;
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//
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static const G4double gLPMconstant;
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//
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static const G4double gXGL[8];
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static const G4double gWGL[8];
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static const G4double gFelLowZet[8];
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static const G4double gFinelLowZet[8];
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//
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static const G4double gXSecFactor;
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static const G4double gEgLPMActivation;
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//
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static std::vector<ElementData*> gElementData;
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static LPMFuncs gLPMFuncs;
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//
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G4bool fIsUseLPMCorrection;
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G4bool fIsUseCompleteScreening;
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//
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G4double fLPMEnergy;
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//
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G4double fParametrizedXSectionThreshold;
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G4double fCoulombCorrectionThreshold;
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//
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G4Pow* fG4Calc;
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G4ParticleDefinition* fTheGamma;
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G4ParticleDefinition* fTheElectron;
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G4ParticleDefinition* fThePositron;
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G4ParticleChangeForGamma* fParticleChange;
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};
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//
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// Bethe screening functions for the elastic (coherent) scattering:
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// Bethe's phi1, phi2 coherent screening functions were computed numerically
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// by using (the universal) atomic form factors computed based on the Thomas-
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// Fermi model of the atom (using numerical solution of the Thomas-Fermi
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// screening function instead of Moliere's analytical approximation). The
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// numerical results can be well approximated (better than Butcher & Messel
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// especially near the delta=1 limit) by:
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// ## if delta <= 1.4
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// phi1(delta) = 20.806 - delta*(3.190 - 0.5710*delta)
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// phi2(delta) = 20.234 - delta*(2.126 - 0.0903*delta)
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// ## if delta > 1.4
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// phi1(delta) = phi2(delta) = 21.0190 - 4.145*ln(delta + 0.958)
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// with delta = 136mc^2kZ^{-1/3}/[E(Eg-E)] = 136Z^{-1/3}eps0/[eps(1-eps)] where
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// Eg is the initial photon energy, E is the total energy transferred to one of
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// the e-/e+ pair, eps0 = mc^2/Eg and eps = E/Eg.
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inline
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void G4PairProductionRelModel::ComputePhi12(const G4double delta, G4double &phi1,
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G4double &phi2)
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{
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if (delta > 1.4) {
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phi1 = 21.0190 - 4.145*G4Log(delta + 0.958);
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phi2 = phi1;
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} else {
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phi1 = 20.806 - delta*(3.190 - 0.5710*delta);
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phi2 = 20.234 - delta*(2.126 - 0.0903*delta);
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}
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}
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// Compute the value of the screening function 3*PHI1(delta) - PHI2(delta):
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inline G4double G4PairProductionRelModel::ScreenFunction1(const G4double delta)
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{
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return (delta > 1.4) ? 42.038 - 8.29*G4Log(delta + 0.958)
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: 42.184 - delta*(7.444 - 1.623*delta);
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}
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// Compute the value of the screening function 1.5*PHI1(delta) +0.5*PHI2(delta):
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inline G4double G4PairProductionRelModel::ScreenFunction2(const G4double delta)
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{
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return (delta > 1.4) ? 42.038 - 8.29*G4Log(delta + 0.958)
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: 41.326 - delta*(5.848 - 0.902*delta);
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}
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// Same as ScreenFunction1 and ScreenFunction2 but computes them at once
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inline void G4PairProductionRelModel::ScreenFunction12(const G4double delta,
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G4double &f1, G4double &f2)
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{
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if (delta > 1.4) {
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f1 = 42.038 - 8.29*G4Log(delta + 0.958);
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f2 = f1;
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} else {
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f1 = 42.184 - delta*(7.444 - 1.623*delta);
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f2 = 41.326 - delta*(5.848 - 0.902*delta);
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}
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}
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#endif
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